Covishield v/s Covaxin
- A study was conducted recently on healthcare workers (HCW) to study the real-world effectiveness of vaccination in India.
- The findings confirmed that the Covishield vaccine produced more antibodies than Covaxin.
- Also, seropositivity rates to anti-spike antibodies were significantly higher in Covishield recipients compared to Covaxin after the first dose.
- The study found that a single dose of Covishield elicited about 10 times the antibodies than Covaxin whereas a second dose narrowed the gap somewhat.
- Covishield (the vaccine by Oxford University-AstraZeneca) is based on the viral-vectored platform.
- Covaxin (jointly developed by Bharat Biotech and the Indian Council of Medical Research), is an inactivated vaccine.
A vector, in infectious disease biology, is what works as a vehicle to transport a disease-causing agent.
In viral-vectored vaccines, a virus is used to carry the target antigen gene into human cells.
Covishield uses a chimpanzee adenovirus (AZD1222 or ChAdOx1), which carries the SARS-CoV-2 spike protein.
The chimpanzee adenovirus has been used because humans will not have pre-existing antibodies to this adenovirus.
Inactivated or killed vaccines
- Pathogens (viruses or bacteria) that cannot multiply cannot cause disease. So inactivating a virus or bacteria, using chemicals like formalin, can convert them into a safe immunogen.
- Because inactivated viruses or bacteria do not multiply, we may need to use multiple doses of the vaccine and also give another substance to improve the immune response — this is called an adjuvant.
- The most common adjuvant is the alum but shark oil suspensions and a few others are also used.